The overall aim of this proposal is to further investigate age-related alterations in the cardiovascular and skeletal muscular systems. A more sedentary lifestyle, as well as the process of aging, per se, have each been hypothesized as possible explanations for the decline in functional capacity that occurs with advanced age. Additionally, it has been suggested on the basis of minimal evidence that the capability of optimally regaining functional losses by exercising is reduced as aging progresses. The proposed experiments will investigate the effects of aging upon cardiovascular functional capabilities, determine whether age-related changes may be altered by dynamic exercise training, and determine whether chronic exercise accelerates, attenuates, or reverses declines in cardiovascular function that occur during the aging process. Cross-sectional and longitudinal studies, utilizing mature adult and senescent beagles, will be used to determine hemodynamic and regional blood flow responses to stress on an acute and chronic basis. In addition, the significance of adaptive responses of the sympathoadrenal and adrenergic systems upon age-related changes in myocardial function will be investigated before and after chronic exercise. Specific questions to be addressed include: 1) Do functional alterations occur in the myocardium with advanced age? 2) Do significant changes occur in the peripheral circulation during the aging process? 3) Do age-related reductions in endurance occur in skeletal muscle? 4) Do alterations during aging in the adrenergic and sympathoadrenal systems effect functional capacity? 5) What types of adaptation occur within the cardiovascular and skeletal muscular systems in response to dynamic exercise training in senescence? 6) Are age-related changes in myocardial, skeletal muscular, peripheral circulatory, sympathoadrenal, and adrenergic systems altered by chronically increased levels of activity? Regional blood flow will be determined by the radioactive microsphere technique, cardiac output by dye dilution, total body oxygen consumption by the product of arteriovenous oxygen difference and cardiac output, and beta-adrenoreceptor numbers and affinity by radioligand binding. Skeletal muscle histochemistry, biochemistry, and morphometrics will also be evaluated. This work is expected to document diminished functional capabilities that occur with advanced age, as well as the types of adaptive responses that result after chronic exercise. This knowledge may be clinically useful when considering activity levels and dynamic exercise training for the elderly.